Iaxclient is an open source, multiplatform library for creating telephony
solutions that interoperate with Asterisk, the Open Source PBX.

Although asterisk supports other VOIP protocols (including SIP, and
with patches, H.323), IAX's simple, lightweight nature gives it several
advantages, particularly in that it can operate easily through NAT and
packet firewalls, and it is easily extensible and simple to understand.

This requires portaudio, speex, and libvidcap.